New compositions or vaccines with an improved immunogenicity are always needed. As one strategy, adjuvants have been used to try and improve the immune response raised to any given antigen.
WO05/014110 discloses compositions which comprise a) a liposome b) at least one A-type CpG, wherein the A-type CpG is bound to or enclosed by the liposome. Shahum & Thérin [Immunology (1988) 65:315-317] disclose compositions comprising bovine serum albumin that is either free, encapsulated in liposomes or covalently linked to the liposomal surface using the hetero-bifunctional reagent N -Succinimidyl 3-(2-pyridyldithio)-propionate (SPDP). Using this method of classical conjugation the antigen is directly and covalently attached to the liposomes at an early stage of formulation. This attachment is not reversible unless enzymatically or chemically degraded. On the other hand, the encapsulation method is associated with a risk of denaturation and/or degradation of the antigen.
Alternative methods consist of the binding of antigens to ionically charged liposomes via electrostatic interactions. The HSV antigen gB was complexed to the cationic lipid DOTAP and successfully used to induce an immune response in vaccinated mice, in particular a CTL response (Walker et al. 1992-PNAS, 89: 7915-7918). HBsAg combined with the cationic lipid DC-chol generated an improved and balanced immunity able to overcome the unresponsiveness of mice to hepatitis B vaccine (Brunel at al. 1999.Vaccine 17: 2192-2203).
There is still a need for improved vaccine and immunogenic compositions that provide a suitable immune response.